The proposed research will analyze changes that occur in the microcirculatory patterns of the developing interdigit of the chick embryo foot. The changes will be compared with the cell death patterns associated with the formation of free digits. Studies will include autoradiographic determination of the macromolecular syntheses patterns and fine structure analysis of the cells served by the microvasculature and which are fated to die. The experiments are also designed to ascertain differences in mitotic rates between the digit and interdigit cells. Experiments will be continued isolating nuclei from prospectively necrotic cells of the posterior necrotic zone of the chick wing bud, to determine if there are changes in histone syntheses that are associated with the irreversible commitment of these cells to die. BIBLIOGRAPHIC REFERENCES: Pollak, R.D. and Fallon, J.F. 1976 Autoradiographic analysis of macromolecular synthesis in prospectively necrotic cells of the chick wing bud. II. Nucleic Acids. Exp. Cell Res. 100:15-22. Cameron, J.A. and Fallon, J.F. 1977 The absence of cell death during development of free digits in Amphibians. Develop. Biol. In Press.